When and how ofter should I core aerate?

I believe I read somewhere that core aeration should be done at least once a year. My question, is when. Is now a good time to core aerate. Our temps in South Carolina have been in the mid 20s to mid 30s at night and mid 50s during the day. Please advise. Thanks.

I have customers that want ti in spring and some that want it in fall so i do both, a couple get it done and spring and fall tried to tell them once is good but they insist so good for me, in michigan i start aerations in april